The term HUSNG is an abbreviation for Heads-Up Sit and Go, a poker tournament format in which only two players play against each other. In such MTTs, players start with an equal chip amount and play until one of them has all of it.
For example, if you play $22 HUSNG against another player, with $20 going to the buy-in and $2 going to the rake, the winner of the match will get $40. HUSNG tournaments don’t offer the player the option to leave earlier, and players can’t just keep folding like they could in a full-ring poker game. This makes HUSNG tournaments very exciting, as they involve a lot of leveling and aggression.